The present invention relates to microwave reflector antenna and, more specifically, to a microwave reflector antenna for attachment to an aircraft.
Microwave reflector antennas can be used in airborne applications. For example, microwave reflector antennas can be used on an aircraft to allow the aircraft to communicate with other parties. When the microwave reflector antenna is used on an aircraft, the microwave reflector antenna is typically positioned on the crown of the exterior of the aircraft. The positioning of the microwave reflector antenna on the exterior of the aircraft increases the drag of the aircraft as it travels through the atmosphere and exposes the microwave reflector antenna to the harsh environments that the aircraft is exposed to. Therefore, the microwave reflector antennas are typically covered by a radome which completely covers the microwave reflector antenna and reduces the drag caused by positioning the microwave reflector antenna on the exterior of the aircraft.
The radome is designed to cover the microwave reflector antenna and to reduce the drag on the aircraft caused by the microwave reflector antenna. To achieve a reduction in the drag on the aircraft associated with covering a microwave reflector antenna with a radome, the radome is gradually tapered from its peak to its ends. The typical radome will have a length along the aircraft of approximately 10 to 12 inches for every inch of height for which the radome must extend above the aircraft to cover the microwave reflector antenna. The typical microwave reflector antenna requires a radome of approximately 10 to 12 ft. or more in length to cover the microwave reflector antenna.
Because the cost of the radome is proportional to the size of the radome, any reduction in the height of the radome and the resulting length of the radome will result in a cost savings. Additionally, decreasing the size of the radome will also decrease the drag caused by the radome on the aircraft. Therefore, it is desirable to reduce the height of the microwave reflector antenna so that the height of the radome and its resulting length can also be reduced. In a typical application, every inch of reduction in the height of the radome will result in a length reduction of approximately 10 to 12 inches.
The typical microwave reflector antenna has a reflector that is capable of rotating about two different axis. The first axis of rotation is the azimuth axis. Rotation of the reflector about the azimuth axis allows the reflector to rotate 360xc2x0 so that the reflector can point in any direction along the horizon. The second axis of rotation is the elevation axis. Rotation of the reflector about the elevation axis allows the elevation of the reflector to be adjusted so that the reflector can be oriented between the horizon and the sky.
The typical microwave reflector antenna has a stationary or base plate that is attached to the aircraft and remains stationary relative to the aircraft. A rotating plate allows the reflector to rotate about the azimuth axis. The rotating plate and stationary plate are separated by a radial/thrust bearing. The radial/thrust bearing is a separate part that is positioned between the stationary plate and rotating plate and allows the rotating plate to rotate relative to the stationary plate about the azimuth axis. The use of a separate radial/thrust bearing results in an increase in height of the microwave reflector antenna. The increased height thereby increases the aerodynamic drag and increases the size of the radome required to cover the microwave reflector antenna. Therefore, it is desirable to have a bearing that allows the rotary plate to rotate relative to the stationary plate and is of minimal height.
The typical microwave reflector antenna has a rotary joint that is attached to the rotating plate and has an axis of rotation that is aligned with the azimuth axis. The rotary joint allows electric signals to pass between the reflector and the aircraft. The rotary joints are usually several inches in height at a minimum and are placed directly under the reflector. The placement of the rotary joint directly under the reflector raises the height of the microwave reflector antenna several inches and increase the height and size of the radome required to cover the microwave reflector antenna.
The typical microwave reflector antenna also has an azimuth motor that causes the rotation of the reflector about the azimuth axis. The azimuth motor has a pinion gear that engages with teeth that are stationary relative to the rotating plate and allows the azimuth motor to cause the rotary plate to rotate about the azimuth axis. The location of teeth and the azimuth motor can effect the overall height of the microwave reflector antenna and the associated size of the required radome.
Therefore, what is needed is a microwave reflector antenna that has a minimum height so that the radome necessary to cover the microwave reflector antenna is also of a minimum size.
The microwave reflector antenna of the present invention is for use on the exterior of an aircraft. The microwave reflector antenna is designed to achieve a minimal height so that a radome that covers the microwave reflector antenna can be of minimal size.
The airborne microwave reflector antenna of the present invention generally comprises a stationary plate attached to the aircraft so that the stationary plate does not move relative to the aircraft. There is a rotary plate that is capable of rotating relative to the stationary plate about an azimuth axis. A rotary joint is attached to the rotary plate. The rotary joint has an axis of rotation that is aligned with the azimuth axis so that rotation of the rotary plate causes the rotary joint to rotate about the azimuth axis. A reflector is attached to the rotary plate and rotates about the azimuth axis with the rotation of the rotary joint. The reflector is positioned adjacent to the rotary joint so that the axis of rotation of the rotary joint does not intersect the reflector. The azimuth motor selectably causes the rotary plate to rotate about the azimuth axis. The locating of the reflector adjacent the rotary joint allows the height of the rotary joint to not affect the height of the reflector and the subsequent height of the microwave reflector antenna. That is, the reflector is not positioned directly above the rotary joint and, as a result, can be positioned closer to the rotating plate and reduce the overall height of the microwave reflector antenna.
In another aspect of the present invention, a microwave reflector antenna has individual loose ball bearings positioned between the stationary plate and the rotary plate. The individual loose ball bearings allow the rotary plate to rotate relative to the stationary plate about the azimuth axis. The individual loose ball bearings are integrated into the stationary and rotary plates and are used in place of the separate radial/thrust bearing used in a typical microwave reflector antenna. By integrating the individual loose ball bearings directly into the stationary and rotary plates, the use of a separate radial/thrust bearing is avoided and a reduction in the height of the microwave reflector antenna can be achieved.
In another aspect of the invention, a microwave reflector antenna has a stationary plate with gear teeth machined into the stationary plate. The azimuth motor is attached to the rotary plate. The azimuth motor has a pinion gear with teeth that are complementary to the gear teeth on the stationary plate. The azimuth motor is attached to the rotary plate with the teeth on the pinion gear engaged with the gear teeth on the stationary plate. The azimuth motor can be selectively operated to selectively cause the rotary plate to rotate about the azimuth axis by rotating the pinion gear. The integration of the gear teeth into the stationary plate eliminates the need for a separate gear to be attached to the stationary plate.
The reduction in height of the airborne microwave reflector antenna provided by the present invention allows for the size of the radome that covers the microwave reflector antenna to be reduced. The reduction in the size of the radome reduces costs and decreases the drag on the aircraft caused by the microwave reflector antenna being attached to the aircraft.
Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention.